1. Field of the Invention
The invention relates in general to a paper pick-up mechanism, and more particularly to a paper pick-up mechanism for a feeder of an image forming apparatus. The image forming apparatus could be a scanner, a copier, a printer, a fax machine or a multi-function peripheral.
2. Description of the Related Art
A conventional feeder has a pick-up mechanism for sequentially feeding a stack of sheets placed on a tray.
As shown in FIG. 8, The pick-up mechanism 90 includes a pick-up roller 91 and a separation roller 92. A motor (not shown) provides a torque to a rotating shaft 922 of the separation roller 92. A gear set 93 is disposed between the rotating shaft 912 of the pick-up roller 91 and a rotating shaft 922 of the separation roller 92 to transmit the torque to the pick-up roller 91. When the sheet-feeding operation is performed, the separation roller 92 and the pick-up roller 91 are rotated in a sheet-feeding direction. When the sheet-feeding operation ends, the rotating shaft 922 of the separation roller 92 and the rotating shaft 912 of the pick-up roller 91 are rotated in a direction opposite to the sheet-feeding direction.
It is to be noted that a torsional spring 94 could be mounted on the rotating shaft 912 of the pick-up roller 91, so the torsional spring 94 generates a lateral force to a frame 95 supporting the rotating shafts 912 of the pick-up roller 91 and the separation roller 92 to lift the pick-up roller 91 away from the tray (not shown) as the rotating shaft 922 of the separation roller 92 is rotated in the direction opposite to the sheet-feeding direction. However, when the sheet-feeding operation ends, the motor, in order to lift up the pick-up roller 91 and to keep the pick-up roller 91 away from the tray, has to continuously provide the torque to drive the rotating shaft 922 of the separation roller 92 in a reverse direction and has to output a power in addition to the power outputted for the lifting of the pick-up roller 91.
In addition, the pick-up mechanism may be further equipped with a one-way device.
U.S. Pat. No. 6,390,463 discloses a paper pick-up mechanism having two spring-type one-way clutches. The two clutches are serially mounted on a rotating shaft of a separation roller and disposed outside a frame. The rotating shaft has many separated sections to be respectively coupled to the two one-way clutches. Because the two one-way clutches are mounted on the rotating shaft with different coiling directions, they have different working directions. When the rotating shaft of the separation roller is rotated in a direction opposite to the sheet-feeding direction, the one-way clutches and the multi-section rotating shaft generate an action force to lift up the pick-up roller and the frame.
However, the clutches are disposed outside the frame, so the clutches may interfere with other elements of the image forming apparatus or the feeder when the clutches are assembled in the image forming apparatus or the feeder. Also, the two one-way clutches in series cannot be easily assembled with the multi-section rotating shaft.